The long-term objectives of this proposal are to extend our knowledge of the tissue interactions involved in tooth root development and thereby understand the processes involved in the generation of the periodontal ligament attachment. Toward this goal it is proposed to investigate the biological mechanism involved in cementoblast induction. This research is based upon the hypothesis that cementoblast induction results from an interaction between cells and a basement membrane present on the forming root surface. Further, that the cells that are in contact with this matrix and play a role in its mineralization (and hence intermediate cementum formation) are former cells of the epithelial root sheath. The first two specific aims address the first part of this hypothesis and are; to investigate the inductive capabilities of the first-formed root matrix from developing mandibular molars of mice in tissue separation and recombination experiments using a variety of substrates and responding cell populations; and to ascertain if and when the epithelial root sheath secretes enamel proteins during cementogenesis using poly and monoclonal antibodies directed against amelogenins and enanelninsby electron immunohistochemistry. Three specific aims address the later part of the hypothesis; to examine in vivo the epithelial-mesenchymal transformation that occurs in cells of the epithelial root sheath by ultrastructural, electron immunohistochemical and in situ hybridization techniques; to duplicate this epithelial-mesenchymal transformation in vitro and to monitor phenotypic change by immunohistochemistry and cytoplasmic dot blot hybridization; and, to determine whether in vitro transformed epithelial root sheath cells express a phenotype in common with other mineralizing tissue cells. The final specific aim is to continue the examination of the morphological events associated with cementogenesis throughout all stages of root development by transmission electron microscopy. Data obtained from these studies will provide valuable information not only to increase our understanding of tissue interactions in development but also they will be invaluable in designing new clinical approaches to the treatment of teeth affected by disease or trauma.